1. Field of the Invention
The present invention relates to a data communication system, more particularly, improvement of an efficiency of use of a network system.
2. Description of the Related Art
A conventional network system of the type of circuit switching, which is known by the telephone or facsimile etc., transmits data according to a way as shown in FIG. 1. First, transmission side calls to reception side, the transmission side acquires a communication line (we will call it to term `circuit`) when the circuit is not acquired by another pair of transmission/reception media. And the transmission side transmits the data to the reception side through the acquired circuit. If the transmission of the data is finished, then the acquired circuit is released. To take an instance as the telephone for understanding the above way, first, one person make a telephone call, if the other party is not situation of while the telephone call, the circuit is acquired by way of having the telephone call by the other party. And if the telephone call is finished, then the circuit is released by way of hanging up the receiver.
However, as shown in FIG. 1B, after the circuit is acquired by the above way, it may happen that the reception of the transmitted data cannot be continued before the data transmission is finished. For example, in the facsimile, if paper for printing runs out during the reception of the transmitted data, the reception of the transmitted data is stopped. And in a computer communication, if a capacity of a buffer memory becomes not enough during the reception of the transmitted data, transmitted data then cannot be received, and a transmission error is caused at the transmission side. In consequence, an effort of the transmission operator for the computer communication and the communication fee is wasted. Especially, when the quantity of data to be transmitted is large, then the waste is a heavy burden to the transmission operator.
And, the network system of the type of circuit switching, generally, has two-communication systems which are the system for transmitting data and the system for controlling the circuit acquisition etc. The communication system for control uses a relatively narrow frequency band, and the system has a lot of circuits, but the system for transmitting data a relatively wide frequency band, example 100 Mbps, and the system does not have many circuits. Hence, if are operator monopolizes the network circuit for transmitting the data after causing the transmission error, then the another operator loses a chance of using the network circuit, and as a result, the efficiency of use drops.